Re: [PATCH 03/15] block: add an API to atomically update queue limits

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+
+int blk_validate_limits(struct queue_limits *lim)
+{
+	unsigned int max_hw_sectors;
+
+	if (!lim->logical_block_size)
+		lim->logical_block_size = SECTOR_SIZE;

nit: This function is doing a bit more than validating, as the function name suggests

+
+	if (!lim->physical_block_size)
+		lim->physical_block_size = SECTOR_SIZE;
+	if (lim->physical_block_size < lim->logical_block_size)
+		lim->physical_block_size = lim->physical_block_size;
+
+	if (!lim->io_min)
+		lim->io_min = SECTOR_SIZE;
+	if (lim->io_min < lim->physical_block_size)
+		lim->io_min = lim->physical_block_size;
+
+	if (!lim->max_hw_sectors)
+		lim->max_hw_sectors = BLK_SAFE_MAX_SECTORS;
+	if (WARN_ON_ONCE(lim->max_hw_sectors < PAGE_SIZE / SECTOR_SIZE))
+		return -EINVAL;

The WARN_ON_ONCE usage is odd, as it will only ever WARN once for a specific q, while other queues associated with other drivers may have the same limit issue. But I suppose if one issue is fixed, then the other will make itself known...

+
+	lim->max_hw_sectors = round_down(lim->max_hw_sectors,
+			lim->logical_block_size >> SECTOR_SHIFT);
+
+	max_hw_sectors = min_not_zero(lim->max_hw_sectors,
+				lim->max_dev_sectors);
+	if (lim->max_user_sectors) {
+		if (lim->max_user_sectors > max_hw_sectors ||
+		    lim->max_user_sectors < PAGE_SIZE / SECTOR_SIZE)
+			return -EINVAL;
+		lim->max_sectors = min(max_hw_sectors, lim->max_user_sectors);
+	} else {
+		lim->max_sectors = min(max_hw_sectors, BLK_DEF_MAX_SECTORS_CAP);
+	}
+

+/**
+ * queue_limits_commit_update - commit an atomic update of queue limits
+ * @q:		queue to update
+ * @lim:	limits to apply
+ *
+ * Apply the limits in @lim that were obtained from queue_limits_start_update()
+ * and updated by the caller to @q.
+ *
+ * Returns 0 if successful, else a negative error code.
+ */
+int queue_limits_commit_update(struct request_queue *q,
+		struct queue_limits *lim)
+	__releases(q->limits_lock)
+{
+	int error = blk_validate_limits(lim);
+
+	if (!error) {
+		q->limits = *lim;

this is duplicating what blk_alloc_queue() does

+		if (q->disk)
+			blk_apply_bdi_limits(q->disk->bdi, lim);
+	}
+	mutex_unlock(&q->limits_lock);
+	return error;
+}
+EXPORT_SYMBOL_GPL(queue_limits_commit_update);
+
  /**
   * blk_queue_bounce_limit - set bounce buffer limit for queue
   * @q: the request queue for the device
diff --git a/block/blk.h b/block/blk.h
index 1ef920f72e0f87..58b5dbac2a487d 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -447,6 +447,7 @@ static inline void bio_release_page(struct bio *bio, struct page *page)
  		unpin_user_page(page);
  }
+int blk_validate_limits(struct queue_limits *lim);
  struct request_queue *blk_alloc_queue(int node_id);
int disk_scan_partitions(struct gendisk *disk, blk_mode_t mode);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 4a2e82c7971c86..5b5d3b238de1e7 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -473,6 +473,7 @@ struct request_queue {
struct mutex sysfs_lock;
  	struct mutex		sysfs_dir_lock;
+	struct mutex		limits_lock;
/*
  	 * for reusing dead hctx instance in case of updating
@@ -861,6 +862,28 @@ static inline unsigned int blk_chunk_sectors_left(sector_t offset,
  	return chunk_sectors - (offset & (chunk_sectors - 1));
  }
+/**
+ * queue_limits_start_update - start an atomic update of queue limits
+ * @q:		queue to update
+ *
+ * This functions starts an atomic update of the queue limits.  It takes a lock
+ * to prevent other updates and returns a snapshot of the current limits that
+ * the caller can modify.  The caller must call queue_limits_commit_update()
+ * to finish the update.
+ *
+ * Context: process context.  The caller must have frozen the queue or ensured
+ * that there is outstanding I/O by other means.
+ */
+static inline struct queue_limits
+queue_limits_start_update(struct request_queue *q)
+	__acquires(q->limits_lock)
+{
+	mutex_lock(&q->limits_lock);
+	return q->limits;
+}
+int queue_limits_commit_update(struct request_queue *q,
+		struct queue_limits *lim);

It ain't so nice that the code for queue_limits_start_update() and queue_limits_commit_update() pair are in separate files.

+
  /*
   * Access functions for manipulating queue properties
   */





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